Suspendable CSMA / CA for IEEE 802.15.4 systems to reduce packet discards caused by backoff failures

Abstract

A computer-implemented method for an IEEE 802.15.4 device is provided based on a suspendable carrier sense multiple access with collision avoidance (CSMA / CA) control program and a standard CSMA / CA control program for an IEEE 802.15.4 network consisting of IEEE 802.15.4 devices. The computer-implemented method is provided on the IEEE 802.15.4 device and causes a processor of the IEEE 802.15.4 device to perform steps including determining permission for back-off suspend and an intention of the IEEE 802.15.4 device to execute a back-off suspend, and selecting a suspendable CSMA / CA control program if back-off suspend is permitted and the IEEE 802.15.4 device intends to execute a back-off suspend. The suspendable CSMA / CA control program is configured to perform active CCA within each unit backoff period, suspend backoff if the channel is detected to be busy, perform CCA if the backoff is completed, transmit a frame if the detected channel condition is clear, increment a number of backoffs (NB) if the detected channel condition is busy, determine whether NB exceeds a threshold macMaxCSMABackoffs, increment a number of retransmissions (NR) if NB exceeds the threshold macMaxCSMABackoffs, and discard the frame if NR exceeds a threshold macMaxFrameRetries.

Description

[Technical Field]

[0001] The present invention relates generally to channel access in wireless communication networks, and more particularly to channel access in IEEE 802.15.4 systems. (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of priority under 35 U.S.C. § 120 of co-pending U.S. Nonprovisional Patent Application Serial No. 18 / 474,291, filed September 26, 2023, which claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 465,936, filed May 12, 2023, the contents of each of which are incorporated herein by reference in their entirety and the benefit of each of which is claimed in full. [Background technology]

[0002] With the advent of 5G and beyond communication technologies, consumer Internet of Things (IoT) devices are becoming more capable of supporting IoT applications. The size of IoT networks is rapidly increasing, from hundreds to tens of thousands. As more and more devices compete for channel access, the efficiency of channel access mechanisms becomes a critical issue that needs to be addressed.

[0003] In addition, to meet the requirements of diverse IoT applications, a wide range of wireless communication technologies have been developed to address various IoT applications, such as smart meters and smart cities. However, spectrum allocation is constrained. Therefore, multiple heterogeneous wireless networks may be forced to coexist and compete for spectrum resources. Therefore, interference between networks using different communication technologies may make channel access more contentious, which further increases the requirements for the efficiency of channel access mechanisms.

[0004] IEEE 802.15.4 is a commonly referenced family of wireless standards developed for indoor and outdoor applications. The IEEE 802.15.4 standard is widely implemented in commercial products such as Bluetooth® and smart meters. IEEE 802.15.4 is designed to operate in sub-1 GHz (S1G) and 2.4 GHz bands; for example, IEEE 802.15.4g can operate in both sub-1 GHz and 2.4 GHz bands. An IEEE 802.15.4 network may consist of hundreds to thousands of devices, which compete for channel access and cause data loss due to backoff failure. IEEE 802.15.4 uses a carrier sense multiple access with collision avoidance (CSMA / CA) mechanism for channel access. For each channel access attempt, IEEE 802.15.4 does not perform clear channel assessment (CCA) during the backoff period and performs CCA only after the backoff process is complete. This strategy works well in low-traffic networks, but it does not work well in high-traffic networks, especially when coexisting with more aggressive interfering networks such as IEEE 802.11 networks. Therefore, a new channel access mechanism needs to be provided for IEEE 802.15.4 systems.

[0005] In the IEEE 802.15.4 CSMA / CA mechanism, the term backoff means a delay. Therefore, the plural form of backoff means multiple delays. Consequently, backoff time means a delay time. In addition, a backoff failure means a failure of the CSMA / CA algorithm, which returns a success or failure status. Furthermore, the data structure used to contain data has different names at different layers; for example, the data structure is called a packet at the network layer and a frame at the MAC layer.

[0006] The IEEE 802.15.4 CSMA / CA algorithm is divided into two branches, namely, the time-synchronized channel hopping (TSCH) branch and the non-TSCH branch, as shown in Figure 3. The TSCH mechanism uses time division multiple access (TDMA) to ensure there is no transmission contention between devices in an IEEE 802.15.4 network. The TSCH mechanism can use CCA to detect transmissions from interfering networks, such as another IEEE 802.15.4 network or an IEEE 802.11 network. The non-TSCH branch uses CSMA / CA, and the efficiency of the CSMA / CA mechanism should be improved.

[0007] Therefore, it is desirable for IEEE 802.15.4 to provide a new channel access method to achieve better performance. Summary of the Invention

[0008] Some embodiments are based on the recognition that the IEEE 802.15.4 CSMA / CA mechanism is designed for low data rate and low power devices where energy conservation is important. Therefore, the IEEE 802.15.4 CSMA / CA mechanism does not support back-off suspend and is therefore not well suited to emerging devices that are not energy constrained, such as electric smart meters.

[0009] To that end, one objective of some embodiments is to provide a suspendable CSMA / CA mechanism for IEEE 802.15.4 to support backoff suspend, which can reduce the probability of packet drops caused by backoff failures as shown in FIG. 4.

[0010] Therefore, some embodiments of the present invention provide a suspendable CSMA / CA mechanism in the IEEE 802.15.4 standard for non-TSCH channel access, where CCA is actively performed within each unit backoff period and the backoff process is suspended when the channel is detected to be busy.

[0011] Some embodiments are based on the recognition that in non-slotted CSMA / CA, the first backoff period and CCA period can start at any time, but in slotted CSMA / CA, the first backoff period and CCA period must start at a backoff period boundary.

[0012] Therefore, backoff suspend must not violate the backoff boundary rules in slotted CSMA / CA.

[0013] Some embodiments are based on the recognition that energy conservation is important for battery-powered devices. However, devices such as electric smart meters connected to the power line are not energy constrained. These devices may actively perform CCA to increase their channel access opportunities and reduce the probability of backoff failure.

[0014] Some embodiments are based on the recognition that the threshold macMaxCSMABackoffs defined in the IEEE 802.15.4 CSMA / CA mechanism, i.e., the maximum number of times the CSMA / CA algorithm can be delayed, is designed to limit the number of backoffs (NB). If NB exceeds the threshold macMaxCSMABackoffs, the packet is discarded. As more and more devices compete for channel access, NB may quickly reach the threshold macMaxCSMABackoffs. As a result, IEEE 802.15.4 packets may be discarded.

[0015] Therefore, suspendable CSMA / CA enables backoff suspension, which then slows down the growth of NB by suspending the backoff process to avoid packet drops when NB exceeds a threshold macMaxCSMABackoffs. In suspendable CSMA / CA, CCA after backoff is performed only if the channel is idle for the last unit backoff period, rather than blindly performing CCA after backoff completion. Blind CCA increases the probability of backoff failure, as shown in Figure 4.

[0016] Some embodiments are based on the recognition that suspendable CSMA / CA may allow the backoff process to last for an unlimited amount of time, which is undesirable.

[0017] To that end, the suspendable CSMA / CA mechanism defines a maximum backoff time (BT) threshold, macSuspendedCSMAMaxTime, which is the maximum time the suspendable CSMA / CA algorithm can delay in backoff. If BT exceeds the threshold, macSuspendedCSMAMaxTime, the suspendable CSMA / CA algorithm terminates with a failure status.

[0018] According to some embodiments of the present invention, there is provided a computer-implemented method for executing a suspendable carrier sense multiple access with collision avoidance (CSMA / CA) control program in an IEEE 802.15.4 network comprised of IEEE 802.15.4 devices, the computer-implemented method causing a processor of the IEEE 802.15.4 device to perform steps including determining permission for back-off suspend by receiving an association response command from a network manager of the IEEE 802.15.4 network, obtaining the IEEE 802.15.4 device's intention to execute back-off suspend contained in a suspendable CSMA / CA field of the association request command, and if the back-off suspend is permitted and the IEEE 802.15.4 device intends to execute the back-off suspend, selecting a suspendable CSMA / CA control program from memory, the suspendable CSMA / CA control program executing an active CCA within each unit back-off period, and if the channel status of the IEEE 802.15.4 network is busy, the suspendable CSMA / CA control program executes ... and determining whether the backoff time exceeds a predefined threshold, macSuspendedCSMAMaxTime. The method further causes the processor to perform the steps of: transmitting a data frame if the detected channel status is the free state, and incrementing a number of backoffs (NB) if the detected channel status is busy; determining whether the NB exceeds a threshold, macMaxCSMABackoffs; incrementing a number of retransmissions (NR) if the NB exceeds the threshold, macMaxCSMABackoffs; and discarding the data frame if the NR exceeds a threshold, macMaxFrameRetries.

[0019] Some embodiments of the present invention further provide a network device for performing suspendable carrier sense multiple access with collision avoidance (CSMA / CA) in an IEEE 802.15.4 network, the network device comprising: a processor; and a memory configured to store a CSMA / CA mode control program, the CSMA / CA mode control program causing the processor to perform the following steps: determining permission for back-off suspend by receiving an association response command from a network manager of the IEEE 802.15.4 network; obtaining the IEEE 802.15.4 device's intention to perform back-off suspend contained in a suspendable CSMA / CA field of the association request command; and selecting a suspendable CSMA / CA control program from the memory if the back-off suspend is permitted and the IEEE 802.15.4 device intends to perform the back-off suspend; the suspendable CSMA / CA control program performs an active CCA within each unit back-off period; and and determining whether the backoff time exceeds a predefined threshold macSuspendedCSMAMaxTime, wherein the CSMA / CA mode control program further causes the processor to perform the steps of: transmitting a data frame if the detected status is the free state; incrementing a number of backoffs (NB) if the detected channel status is busy; determining whether the NB exceeds a threshold macMaxCSMABackoffs; incrementing a number of retransmissions (NR) if the NB exceeds the threshold macMaxCSMABackoffs; and discarding the data frame if the NR exceeds a threshold macMaxFrameRetries.

[0020] The present invention will now be described more fully with reference to the accompanying drawings, in which: The drawings shown are not necessarily to scale, with emphasis generally being placed upon illustrating the principles of embodiments of the present disclosure. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic diagram of an IEEE 82.15.4 network according to some embodiments of the present invention. [Figure 2A] 1 illustrates an IEEE 802.15.4 data transmission flow diagram and transmission status reporting to upper layers according to an embodiment of the present invention. [Figure 2B] 2 is a schematic diagram of the structure of IEEE 802.15.4 CSMA / CA devices participating in forming the network of FIG. 1 according to an embodiment of the present invention. [Figure 3] FIG. 1 illustrates the standard Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) algorithm specified in IEEE 802.15.4-2020, in accordance with an embodiment of the present invention. [Figure 4] 1 shows that the standard IEEE 802.15.4 CSMA / CA algorithm according to an embodiment of the present invention can cause more backoff failures compared to the suspendable IEEE 802.15.4 CSMA / CA algorithm. [Figure 5A] 1 illustrates a flowchart of a suspendable carrier sense multiple access / collision avoidance (CSMA / CA) mechanism for IEEE 802.15.4 supporting suspendable backoff, according to an embodiment of the present invention. [Figure 5B] 1 shows a flowchart of a suspendable carrier sense multiple access / collision avoidance (CSMA / CA) method for non-slotted IEEE 802.15.4 networks, in accordance with an embodiment of the present invention. [Figure 5C] 1 illustrates a flowchart of a suspendable carrier sense multiple access / collision avoidance (CSMA / CA) method for slotted IEEE 802.15.4 networks, in accordance with an embodiment of the present invention. [Figure 6] FIG. 2 illustrates the structure of a unit backoff period as defined in IEEE 802.15.4 according to an embodiment of the present invention. [Figure 7A] FIG. 10 illustrates an example of performing active CCA during the entire unit backoff period according to an embodiment of the present invention. [Figure 7B] FIG. 10 illustrates an example of performing active CCA in a CCA period located within a unit backoff period according to an embodiment of the present invention. [Figure 7C] 1 illustrates an example of performing active CCA in a CCA period starting at a boundary of a unit backoff period according to an embodiment of the present invention. [Figure 8] FIG. 1 illustrates an example of backoff suspend implementation provided in a suspendable CSMA / CA mechanism according to an embodiment of the present invention. [Figure 9A] 10 illustrates a Capability Information field of the inventive Associate Request command according to an embodiment of the present invention. [Figure 9B] 10 illustrates a capability information field of the inventive DSME associate request command according to an embodiment of the present invention. [Figure 9C] 10 illustrates an association status field of the inventive association response command, according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] Various embodiments of the present invention will now be described with reference to the drawings. It should be noted that the drawings are not drawn to scale, and that elements of similar structure or function are represented by similar reference numerals throughout the drawings. It should also be noted that the drawings are intended only to facilitate the description of particular embodiments of the present invention. They are not intended as an exhaustive description of the invention or as limitations on the scope of the invention. In addition, aspects described in connection with a particular embodiment of the present invention are not necessarily limited to that embodiment, but may be practiced in any other embodiment of the present invention.

[0023] The IEEE 802.15.4 standard family is a widely used wireless technology for various indoor and outdoor applications, for example, IEEE 802.15.4g is a standard in the IEEE 802.15.4 standard family designed for outdoor wireless smart utility networks (Wi-SUN), where electricity smart meters are not energy constrained.

[0024] 1 shows a schematic diagram of an IEEE 802.15.4 network 100 including a personal area network coordinator (PANC) 101 and associated nodes. The PANC and the nodes communicate using IEEE 802.15.4 wireless links 103.

[0025] The topology of an IEEE 802.15.4 network can be star, mesh, or tree. For example, the IEEE 802.15.4 network 100 shown in FIG. 1 is a tree topology. In some cases, the IEEE 802.15.4 network 100 can be an IEEE 802.15.4-based smart meter network configured as a tree topology. Note that the connections in the tree topology can change depending on the communication conditions. In addition, not all nodes need to have a direct connection with the PANC 101. In other words, an IEEE 802.15.4 node can communicate with the PANC 101 in a multi-hop manner. For example, the IEEE 802.15.4 node 104 can communicate with the PANC 101 via an intermediate IEEE 802.15.4 node 102.

[0026] 2A shows the IEEE 802.15.4 data frame transmission procedure 200. The IEEE 802.15.4 MAC sets the number of retransmissions (NR) to 0 (201) and then invokes the CSMA / CA algorithm (202), the standard IEEE 802.15.4-2020 CSMA / CA algorithm is shown in FIG.

[0027] If the CSMA / CA algorithm returns a success status (203), the channel is detected as free, and therefore frame transmission begins (204). If an ACK is not required for the frame (AckTX=0) (205), the IEEE 802.15.4 MAC concludes (207) that the transmission was successful and responds to the upper layer with a transmission success status using the data acknowledgement interface. If an ACK is required (AckTX=1) (205) and an ACK is received within the ACK wait period (206), the IEEE 802.15.4 MAC also concludes (207) that the transmission was successful and responds to the upper layer with a transmission success status using the data acknowledgement interface. If an ACK is required and an ACK is not received within the ACK wait period (206), the IEEE 802.15.4 MAC increments NR by 1 (209) and checks (210) whether NR exceeds the threshold macMaxFrameRetries. If YES, the IEEE 802.15.4 MAC concludes that the frame transmission failed and discards the frame (211). The IEEE 802.15.4 MAC then responds to the upper layer with a NO_ACK status using the data acknowledgement interface. If NR is less than or equal to the threshold macMaxFrameRetries (210), the IEEE 802.15.4 MAC attempts another transmission attempt.

[0028] If the CSMA / CA algorithm returns a failure status (203), the IEEE 802.15.4 MAC checks whether the frame is a unicast frame (208). If not, the IEEE 802.15.4 MAC concludes that the transmission failed and discards the frame (211). The IEEE 802.15.4 MAC then uses the data acknowledge interface to: CHANNELIf the frame is a unicast frame (208), the IEEE 802.15.4 MAC increments the NR by 1 (209) and then checks whether the NR exceeds the threshold macMaxFrameRetries (210). If so, the IEEE 802.15.4 MAC concludes that the transmission failed and discards the frame (211). The IEEE 802.15.4 MAC then uses the data acknowledge interface to CHANNEL It responds to upper layers with a _ACCESS_FAILURE status. If the NR is less than or equal to the threshold macMaxFrameRetries, the IEEE 802.15.4 MAC attempts another transmission attempt.

[0029] 2B shows an example of the structure of an IEEE 802.15.4 device 230 that may include memory 236, a processor 237, a power supply 240, a transceiver 238 including a transmitter, a receiver, and an energy detector, and an RF antenna 239. Additionally, a control program is included in storage 231 in association with memory 236, processor 237, and transceiver 238. Control program 231 includes a CSMA / CA mode control program 233, a standard CSMA / CA program 234, a suspendable CSMA / CA program 235, and a timer 232 used by transceiver 238 to execute CSMA / CA mode control program 233. Depending on the backoff suspend permission and the IEEE 802.15.4 device's 230 intention for backoff suspend, the CSMA / CA mode control program 233 can invoke either a standard IEEE 802.15.4 CSMA / CA program 234 or a suspendable CSMA / CA program 235 .

[0030] 3 shows the standard CSMA / CA algorithm specified in IEEE 802.15.4-2020. An embodiment of the present invention provides suspendable CSMA / CA for non-TSCH IEEE 802.15.4 networks. Therefore, only the non-TSCH branch in FIG. 3 is described below.

[0031] Each device maintains three variables for each transmission attempt: the number of backoffs (NB), the contention window length (CW), and the backoff exponent (BE). NB is the number of times the CSMA / CA algorithm was required to backoff during the current transmission attempt. CW is the number of backoff periods that channel activity must clear before transmission can begin. In addition, a default value of CW is also specified as 2. BE relates to the number of backoff periods a device must wait before attempting to evaluate the channel.

[0032] For non-slotted IEEE 802.15.4 networks, i.e., non-beacon-enabled networks, the standard IEEE 802.15.4 CSMA / CA algorithm initializes NB to 0 and BE to macMinBE. The CSMA / CA algorithm then delays a random number of unit backoff periods, where the random number is in the interval [0, 2 BE -1], and BE starts at macMinBE and increases to macMaxBE. After the random backoff / delay is completed, the CSMA / CA algorithm performs CCA operation. If the channel is detected as free, the CSMA / CA algorithm reports success and frame transmission begins. If the channel is detected as busy, the CSMA / CA algorithm updates NB and BE as follows: NB = NB + 1 and BE = min{BE + 1, macMaxBE}. If NB exceeds the threshold macMaxCSMABackoffs, the CSMA / CA algorithm exits with a failure status. Otherwise, the CSMA / CA algorithm continues, i.e., proceeds to perform another random backoff / delay.

[0033] For slotted IEEE 802.15.4 networks, i.e., beacon-enabled networks, the standard IEEE 802.15.4 CSMA / CA algorithm initializes NB to 0 and CW to CW0. If battery life extension is enabled, BE is set to min{2,macMinBE}. Otherwise, BE is set to macMinBE. The CSMA / CA algorithm then locates a backoff period boundary where the start of each device's first backoff period is aligned with the start of its beacon transmission. At the boundary, the CSMA / CA algorithm delays a random number of unit backoff periods, where the random number is in the interval [0,2 BE The BE is chosen uniformly within [macMaxCSMABackoffs -1], starting from macMinBE and increasing to macMaxBE. After the random backoff / delay is completed, the CSMA / CA algorithm performs a CCA operation on the backoff period boundary. If the channel is free, the CSMA / CA algorithm decrements CW by 1. If CW = 0, the CSMA / CA algorithm reports success and initiates frame transmission. Otherwise, if CW > 0, the CSMA / CA algorithm continues with another CCA on the backoff period boundary. After each CCA, if the channel is busy, the CSMA / CA algorithm updates NB, CW, and BE as follows: NB = NB + 1, CW = CW0, and BE = min{BE + 1, macMaxBE}. If NB exceeds the threshold macMaxCSMABackoffs, the CSMA / CA algorithm exits with a failure status. Otherwise, the CSMA / CA algorithm continues, i.e., proceeds to perform another random backoff / delay.

[0034] For non-TSCH networks, the standard IEEE802.15.4 CSMA / CA algorithm first performs a random backoff / delay no matter how long the channel has been idle. With this "backoff+CCA" based CSMA / CA mechanism, CCA is performed blindly, thus reducing the channel access probability as shown in Figure 4. Packet discard due to failure of IEEE802.15.4 CSMA / CA

[0035] In IEEE 802.15.4, a data frame transmission failure occurs due to a) CSMA / CA failure or b) transmission failure. A CSMA / CA failure occurs when the CSMA / CA algorithm terminates with a failure status because the NB exceeds the threshold macMaxCSMABackoffs, as shown in Figure 2A. A transmission failure occurs due to a failure to transmit a frame or a failure to send an acknowledgment or a late receipt of an acknowledgment. For each CSMA / CA failure or transmission failure, the number of retransmissions (NR) is increased by one. An IEEE 802.15.4 frame is discarded with a status of channel access failure if a CSMA / CA failure causes the NR to exceed the threshold macMaxFrameRetries. An IEEE 802.15.4 frame is discarded with a status of NO_ACK if a transmission failure causes the NR to exceed the threshold macMaxFrameRetries. Other transmissions may cause a CSMA / CA backoff failure, as shown in Figure 4, which may then cause the IEEE 802.15.4 device to discard the packet.

[0036] FIG. 4 illustrates an example of a standard IEEE 802.15.4 CSMA / CA backoff failure caused by another transmission. However, the suspendable CSMA / CA program 235 avoids the backoff failure by suspending the backoff process. In FIG. 4, both the suspendable IEEE 802.15.4 backoff device 401 and the standard IEEE 802.15.4 backoff device 402 receive a data transmission request at time T2 and therefore begin backoff at time T2. They also select the same number of unit backoff periods and therefore need to backoff for the same amount of time. However, at an earlier time T1, the other device 403 received a data transmission request and began backoff. At time T3, the other device 403 ends its backoff and begins CCA operation. At time T4, the other device 403 completes CCA, detects a clear channel, and therefore begins data transmission. The suspendable IEEE 802.15.4 backoff device 401 performs active CCA within each unit backoff period and suspends its own backoff process because it detects the transmission of another device 403. On the other hand, the standard IEEE 802.15.4 backoff device 402 does not suspend its own backoff and completes backoff at time T5, thus performing CCA at time T5. However, at time T5, the other device 403 is still transmitting. As a result, the standard IEEE 802.15.4 backoff device 402 detects a busy channel and returns backoff failure at time T7. Meanwhile, the suspendable IEEE 802.15.4 backoff device 401 detects the end of the other device's transmission at time T6 and resumes the remaining backoff. At time T8, the suspendable IEEE 802.15.4 backoff device 401 completes backoff and starts CCA, which ends at time T9 and reports a free channel. Thus, the suspendable IEEE 802.15.4 backoff device 401 successfully transmits its data at time T9 without a backoff failure.

[0037] FIG. 4 clearly shows that the standard IEEE 802.15.4 CSMA / CA mechanism can cause more packet discards compared to the suspendable IEEE 802.15.4 CSMA / CA mechanism. Suspendable CSMA / CA for IEEE 802.15.4

[0038] Some embodiments of the present invention provide suspendable CSMA / CA for IEEE 802.15.4 to address packet discards due to CSMA / CA failures caused by other transmissions.

[0039] A suspendable CSMA / CA field is defined to enable IEEE 802.15.4 devices to perform suspendable CSMA / CA. A suspendable CSMA / CA field of 1 indicates that backoff suspend is allowed. In this case, the IEEE 802.15.4 device may suspend backoff in the CSMA / CA algorithm. When an IEEE 802.15.4 device intends to perform backoff suspend, it invokes either the non-slotted suspendable CSMA-CA algorithm 504 or the slotted suspendable CSMA-CA algorithm 521, depending on whether the IEEE 802.15.4 network is slotted or not. A suspendable CSMA / CA field of 0 indicates that backoff suspend is not allowed. In this case, the IEEE 802.15.4 device cannot perform backoff suspend in the CSMA / CA algorithm. The default value of the Suspendable CSMA / CA field is 0, ie, the Suspendable CSMA / CA field is initialized to 0 and backoff suspend is not allowed.

[0040] The back-off suspend permission may be determined by a regional regulator or a network manager or an application developer or a combination thereof, for example, in the United States, more spectrum is allocated to IEEE 802.15.4 communications and therefore back-off suspend may not be required, while in Japan, less spectrum is allocated to IEEE 802.15.4 communications and therefore back-off suspend may be required.

[0041] In an IEEE 802.15.4 network, a personal area network coordinator (PANC), i.e., a network manager, and devices can recognize the suspendable CSMA-CA algorithm through the capability information field of the association request command of the present invention shown in Figures 9A and 9B and the association status field of the association response command shown in Figure 9C, where Figure 9A shows the capability information field of the association request command and Figure 9B shows the capability information field of the DSME association request command, where DSME stands for deterministic and synchronous multi-channel extension. More specifically, when an IEEE 802.15.4 device associates with a PANC via an association request command, the device sets the suspendable CSMA / CA bit (bit 5) to 1 in the capability information field of the association request command or the DSME association request command to indicate the device's intention to perform backoff suspend. In response, when the PANC sends an Association Response Command back to the device, it sets the Association Status in the Association Response Command to 0x04 to indicate a suspendable CSMA / CA association success, i.e., association is successful and back-off suspend is permitted. If the devices receive an Association Response Command with an Association Status of 0x04, they set their Suspendable CSMA / CA field to 1. Otherwise, if the Association Status is not 0x04, the Suspendable CSMA / CA field remains 0, i.e., back-off suspend is not permitted. The PANC can determine back-off suspend permission based on the region regulator, or application requirements, or network performance, or the number of devices intended to perform back-off suspend, or a combination thereof.

[0042] Even if the association status in the association response command is 0x04, an IEEE 802.15.4 device may choose not to perform back-off suspend, for example, if there is no traffic congestion or the device energy supply is constrained.

[0043] 5A shows a flowchart of an inventive suspendable CSMA / CA mechanism 500 for IEEE 802.15.4 that supports backoff suspend. The inventive CSMA / CA enables IEEE 802.15.4 devices to perform backoff suspend to avoid packet discards due to channel access failures.

[0044] The suspendable CSMA / CA mechanism of the present invention 500 checks whether the IEEE 802.15.4 network is a TSCH network (501). If yes, the standard CSMA-CA algorithm is invoked. If not, the suspendable CSMA / CA mechanism checks whether the IEEE 802.15.4 network is a slotted network (502). If it is a non-slotted network, the suspendable CSMA / CA mechanism of the present invention checks whether backoff suspend is allowed, i.e., whether the suspendable CSMA / CA field = 1 or 0 (503). If the suspendable CSMA / CA field = 1 and the device intends to perform backoff suspend, the suspendable CSMA / CA mechanism of the present invention proceeds to the non-slotted suspendable CSMA-CA algorithm (504). Otherwise, the suspendable CSMA / CA mechanism invokes the standard CSMA-CA algorithm. For slotted IEEE 802.15.4 networks, the suspendable CSMA / CA mechanism of the present invention checks whether backoff suspend is allowed, i.e., whether the suspendable CSMA / CA field = 1 or 0 (520). If the suspendable CSMA / CA field = 1 and the device intends to perform backoff suspend, the suspendable CSMA / CA mechanism of the present invention proceeds to the slotted suspendable CSMA-CA algorithm (521). Otherwise, the suspendable CSMA / CA mechanism invokes the standard CSMA-CA algorithm.

[0045] 5B shows the non-slotted suspendable CSMA-CA algorithm 504. The non-slotted suspendable CSMA-CA algorithm sets NB=0, BT=0 and BE=macMinBE in 505 and sets [0,2 BE6. The non-slotted suspendable CSMA-CA algorithm then uniformly selects a random number of unit backoff periods within [[[(a,b,c,c,d,e,f,f,f,g,f,g,f,i,n ... The non-slotted suspendable CSMA-CA algorithm checks whether BT exceeds the threshold macSuspendedCSMAMaxTime (519). If not, the non-slotted suspendable CSMA-CA algorithm performs active CCA again (507). In this case, all backoff variables NB, CW, and BE are not updated, so NUBP is not decreased; in other words, backoff is suspended. If BT exceeds the threshold macSuspendedCSMAMaxTime, the non-slotted suspendable CSMA-CA algorithm terminates with a failure status (517). If the channel is idle (508), the non-slotted suspendable CSMA-CA algorithm decrements NUBP by 1 (509). If NUBP 510 is not 0, backoff is not complete. Therefore, the non-slotted suspendable CSMA-CA algorithm waits until the next unit backoff period (514). The non-slotted suspendable CSMA-CA algorithm updates the backoff time BT as BT=BT aUnitBackoffPeriod (518).The non-slotted suspendable CSMA-CA algorithm checks whether BT exceeds the threshold macSuspendedCSMAMaxTime (519). If not, the non-slotted suspendable CSMA-CA algorithm performs active CCA again (507). If BT exceeds the threshold macSuspendedCSMAMaxTime, the non-slotted suspendable CSMA-CA algorithm exits with a failure status (517). Otherwise, if NUBP is 0 (510), backoff is complete. The non-slotted suspendable CSMA-CA algorithm then performs standard CCA (511). If the channel is free (512), backoff is successful (513). Otherwise, if the channel is busy (512), the non-slotted suspendable CSMA-CA algorithm increments NB by 1 (515) and updates BE as BE = min{BE + 1, macMaxBE}. If the NB exceeds a predefined threshold, macMaxCSMABackoffs, 516, the non-slotted suspendable CSMA-CA algorithm fails 517. Otherwise, the non-slotted suspendable CSMA-CA algorithm performs another round of backoffs.

[0046] 5C shows a slotted suspendable CSMA-CA algorithm 521. The slotted suspendable CSMA-CA algorithm sets NB=0, BT=0, and CW=CW0 (522). If battery life extension is enabled (523), BE is set as BE=min{2, macMinBE} (524). Otherwise, BE is set to macMinBE (525). The slotted suspendable CSMA-CA algorithm then determines the location of the backoff period boundary (526). At the backoff period boundary, the slotted suspendable CSMA-CA algorithm determines the location of the backoff period boundary within [0, 2 BEThe slotted suspendable CSMA-CA algorithm then uniformly selects a random number of unit backoff periods within [number of unit backoff periods] (527) and sets the number of unit backoff periods (NUBP) to the selected random number. The suspendable CSMA-CA algorithm then performs active CCA on the backoff period boundary (528), as shown in FIG. 7A or 7C. If the channel is busy (529), the slotted suspendable CSMA-CA algorithm locates the backoff period boundary (532) and updates BT as BT = BT + aUnitBackoffPeriod (unit backoff period) (533). The slotted suspendable CSMA-CA algorithm then checks whether BT exceeds a threshold, macSuspendedCSMAMaxTime (534). If yes, the slotted suspendable CSMA-CA algorithm exits with a failure status (539). If not, the slotted suspendable CSMA-CA algorithm again performs active CCA on the backoff period boundary (528). In this case, all backoff variables NB, CW, and BE are not updated, so NUBP is not decreased; in other words, backoff is suspended. If the channel is idle (529), the slotted suspendable CSMA-CA algorithm decreases NUBP by 1 (530). If NUBP is not 0 (531), backoff is not complete. Therefore, the slotted suspendable CSMA-CA algorithm determines the location of the backoff period boundary ( 532), and updates BT as BT = BT + aUnitBackoffPeriod (533). The slotted suspendable CSMA-CA algorithm checks whether BT exceeds a threshold macSuspendedCSMAMaxTime (534). If yes, the slotted suspendable CSMA-CA algorithm exits with a failure status (539). If not, the slotted suspendable CSMA-CA algorithm runs active CCA again on the backoff period boundary (528). Otherwise, if NUBP 531 is 0, backoff is complete. The slotted suspendable CSMA-CA algorithm then runs standard CCA on the backoff period boundary in 535. If the channel is idle (536), the slotted suspendable CSMA-CA algorithm updates CW as CW = CW - 1 (540). If CW is equal to 0 (541), the slotted suspendable CSMA-CA algorithm succeeds (542). Otherwise, the slotted suspendable CSMA-CA algorithm performs CCA again on the backoff boundary (535). If the channel is busy (536), the slotted suspendable CSMA-CA algorithm updates NB, CW, and BE as follows: NB = NB + 1, CW = CW0, and BE = min{BE + 1, macMaxBE} (537). If NB exceeds a predefined threshold, macMaxCSMABackoffs (538), the slotted suspendable CSMA-CA algorithm fails (539). Otherwise, the slotted suspendable CSMA-CA algorithm performs another round of backoff.

[0047] Important differences between standard and suspendable CSMA / CA algorithms:

[0048] The suspendable CSMA / CA algorithm performs CCA in each unit backoff period, while the standard CSMA / CA algorithm does not perform CCA during the entire backoff process.

[0049] The suspendable CSMA / CA algorithm performs CCA511 or CCA535 only if the channel is detected as free in the most recent unit backoff period, whereas the standard CSMA / CA algorithm performs CCA511 or CCA535 whether the channel is busy or free in the most recent unit backoff period.

[0050] The suspendable CSMA / CA algorithm increases NB only if another transmission starts within a CCA period when CCA511 or CCA535 is running. On the other hand, the standard CSMA / CA algorithm increases NB even if another transmission starts before a CCA period or within a CCA period when CCA511 or CCA535 is running. Therefore, the standard CSMA / CA algorithm has a higher probability of increasing NB, which increases the chance of a backoff failure.

[0051] By implementing active CCA, the suspendable CSMA / CA algorithm has the ability to avoid packet drops caused by interference from non-IEEE 802.15.4 devices, such as IEEE 802.11 devices.

[0052] In summary, a suspendable CSMA / CA algorithm can reduce the probability of backoff failure.

[0053] In the IEEE 802.15.4 standard, the unit backoff period is longer than the CCA period. Figure 6 shows the structure of a unit backoff period, including TurnaroundTime (required time) + CCA period. The CCA period is equal to aCcaTime (CCA time) for all PHYs except SUN PHYs operating in the 920 MHz band, and equal to phyCcaDuration (phyCCA duration) for SUN PHYs operating in the 920 MHz band. This indicates that the CSMA / CA algorithm has multiple options for performing active CCA 507 within the unit backoff period or active CCA 528 on a backoff period boundary. It can perform CCA for the entire unit backoff period or for part of the unit backoff period. Figure 7A shows an example in which the CSMA / CA algorithm performs active CCA for the entire unit backoff period. Figure 7B shows an example in which the CSMA / CA algorithm performs active CCA within a CCA period located within the unit backoff period. This situation applies only to non-slotted suspendable CSMA / CA.,Figure 7C shows an example where the CSMA / CA algorithm,performs active CCA within a CCA period that begins,at the boundary of a unit backoff period.

[0054] FIG. 8 illustrates an example of a non-slotted suspendable CSMA-CA algorithm implementation, involving an IEEE 802.15.4 device 801 and another device 802. The other device 802 may be an IEEE 802.15.4 device or a non-IEEE 802.15.4 device, such as an IEEE 802.11 device. At time T1, the other device receives a data request, so the device 802 begins a first backoff. At time T2, the IEEE 802.15.4 device 801 receives a data request, so it also begins a first backoff. At time T3, the other device 802 completes its first backoff and begins CCA operation. At time T4, the other device 802 terminates CCA and detects that the channel is free. Therefore, the other device 802 begins transmission. At the same time T4, the IEEE 802.15.4 device 801 detects transmission by the other device 802. Therefore, if the other device 802 is an IEEE 802.15.4 device, it suspends its first backoff and performs data reception. At time T5, the other device 802 ends transmission, and the channel becomes vacant. Therefore, the IEEE 802.15.4 device 801 resumes its first backoff. At time T6, the IEEE 802.15.4 device completes its first backoff and starts CCA operation. At time T7, the IEEE 802.15.4 device 801 ends CCA, and the channel becomes vacant. Therefore, it starts data transmission. At the same time, if the other device 802 is an IEEE 802.15.4 device, it starts data reception. Finally, at time T8, the IEEE 802.15.4 device 801 ends data transmission.

[0055] Note that if the other device 802 is a non-IEEE 802.15.4 device, devices 801 and 802 cannot receive data from each other. However, they may interfere with each other. By implementing a suspendable CSMA / CA algorithm, IEEE 802.15.4 device 801 can avoid packet drops caused by interference.

[0056] The above-described embodiments of the present invention can be implemented in any of numerous ways. For example, these embodiments may be implemented using hardware, software, or a combination thereof. If implemented in software, the software code may run on any suitable processor or collection of processors, whether located on a single computer or distributed among multiple computers. Such a processor may be implemented as an integrated circuit, with one or more processors within an integrated circuit component. However, a processor may be implemented using circuitry in any suitable format.

[0057] Also, embodiments of the present invention may be embodied as a method, of which an example is provided. The operations performed as part of the method may be ordered in any suitable manner. Thus, embodiments may be constructed in which operations are performed in an order different from the order shown, which may include performing some operations simultaneously even though the illustrated embodiment shows them as sequential operations.

[0058] Furthermore, the use of ordinal language such as "first," "second," etc. to modify a claim element in a claim does not, by itself, imply a priority, precedence, or order of one claim element over another claim element, or a chronological order in which method actions are performed, but is merely used as a label to distinguish one claim element having a certain name from another element having the same name (except for the use of ordinal language).

[0059] Although the invention has been described by way of examples of preferred embodiments, it is to be understood that various other adaptations and modifications can be made within the spirit and scope of the invention.

[0060] Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the invention.

Claims

1. 1. A computer-implemented method for executing a suspendable carrier sense multiple access with collision avoidance (CSMA / CA) control program in an IEEE 802.15.4 network comprised of IEEE 802.15.4 devices, the method comprising: determining permission for backoff suspend by receiving an association response command from a network manager of the IEEE 802.15.4 network; obtaining a configuration for performing the back-off suspend of the IEEE 802.15.4 device contained in a suspendable CSMA / CA field of an association request command; and if the back-off suspend is permitted and the IEEE 802.15.4 device is configured to perform the back-off suspend, calling and executing a suspendable CSMA / CA control program from memory, wherein the suspendable CSMA / CA control program: performing an active CCA within each unit backoff period; suspending backoff processing when a channel status of the IEEE 802.15.4 network is detected to be busy; restarting the backoff process when the channel status is detected to be empty; Whether the backoff time exceeds a predefined threshold, macSuspendedCSMAMaxTime and determining the number of times ... transmitting a data frame if the detected channel status is said free state, and incrementing a backoff number (NB) if the detected channel status is a busy state; determining whether the NB exceeds a threshold macMaxCSMABackoffs; incrementing the number of retransmissions (NR) if the NB exceeds the threshold macMaxCSMABackoffs; and discarding the data frame if the NR exceeds a threshold macMaxFrameRetries.

2. 2. The method of claim 1, wherein the IEEE 802.15.4 device applies a standard CSMA / CA channel access mechanism when the backoff suspend is not allowed, and the IEEE 802.15.4 device applies a suspendable CSMA / CA channel access mechanism when the backoff suspend is allowed, and the suspendable CSMA / CA channel access mechanism can be a non-slotted suspendable CSMA-CA algorithm or a slotted suspendable CSMA-CA algorithm.

3. 2. The method of claim 1, wherein the backoff suspend is permitted by a network manager of a personal area network coordinator (PANC) based on an area regulator, application requirements, network performance, or the number of IEEE 802.15.4 devices configured to perform the backoff suspend, or a combination thereof.

4. The method described in claim 3, wherein the IEEE 802.15.4 device is granted the backoff suspend permission by the network manager.

5. The method of claim 4 , wherein the IEEE 802.15.4 device chooses not to perform the backoff suspend even if the backoff suspend is permitted.

6. The IEEE 802.15.4 device performs the backoff suspend to execute the active CCA within each of the unit backoff periods, suspends the backoff process when it detects that the channel is busy, and a suspendable CSMA / CA channel access mechanism suspends the backoff process when the number of backoffs exceeds the threshold macMaxCSMABackoffs or the backoff time exceeds the threshold macSuspendedCSMAMaxTime.

10. The method of claim 1, wherein the method fails if

7. The IEEE 802.15.4 device running suspendable CSMA / CA first sets the unit backoff period (NUBP) to a random number in the range [0, 2 ＢＥ -1], and then the active CCA is performed within each of the unit backoff periods, and if the channel is busy, the backoff process is suspended (i.e., NUBP is not decreased), and if the channel is free, the backoff process continues, and the backoff process is completed when NUBP reaches zero.

8. The method of claim 6 , wherein the IEEE 802.15.4 device performs a standard CCA within a CCA period when the number of unit backoff periods (NUBP) reaches zero.

9. 9. The method of claim 8, wherein the IEEE 802.15.4 device transmits data if CCA reports a free channel, and the CSMA / CA algorithm reports a backoff failure if the CCA reports a busy channel and the number of backoffs (NB) is increased by one.

10. 10. The method of claim 9, wherein the CSMA / CA algorithm reports a channel access failure if the number of backoffs (N) exceeds the predefined threshold macMaxCSMABackoffs, and the number of retransmissions (N) is incremented by one when the CSMA / CA algorithm reports a channel access failure.

11. 11. The method of claim 10, wherein the IEEE 802.15.4 MAC discards data if the number of retransmissions (NR) exceeds a threshold macMaxFrameRetries.

12. The method of claim 6 , wherein the IEEE 802.15.4 device can perform the active CCA for the entire unit backoff period or for a portion of the unit backoff period.

13. 1. A network device for performing suspendable carrier sense multiple access with collision avoidance (CSMA / CA) in an IEEE 802.15.4 network, comprising: a processor; and a memory configured to store a CSMA / CA mode control program, the CSMA / CA mode control program causing the processor to: determining permission for backoff suspend by receiving an association response command from a network manager of the IEEE 802.15.4 network; obtaining a configuration of the network device to perform the backoff suspend, the configuration being included in a suspendable CSMA / CA field of an association request command; and if the back-off suspend is permitted and the network device is configured to execute the back-off suspend, calling and executing a suspendable CSMA / CA control program from the memory, wherein the suspendable CSMA / CA control program: performing an active CCA within each unit backoff period; suspending backoff processing when a channel of the IEEE 802.15.4 network is detected to be busy; restarting the backoff process when the channel condition is detected to be clear; Whether the backoff time exceeds a predefined threshold, macSuspendedCSMAMaxTime and determining whether the CSMA / CA mode control program is configured to execute the steps of: transmitting a data frame if the detected status is said idle state, and incrementing a backoff number (NB) if the detected channel status is busy; determining whether the NB exceeds a threshold macMaxCSMABackoffs; incrementing the number of retransmissions (NR) if the NB exceeds the threshold macMaxCSMABackoffs; and discarding the data frame if the NR exceeds a threshold macMaxFrameRetries.

14. 14. The network device of claim 13, wherein the network device applies a standard CSMA / CA channel access mechanism when the backoff suspend is not allowed, and the network device applies a suspendable CSMA / CA channel access mechanism when the backoff suspend is allowed, and the suspendable CSMA / CA channel access mechanism can be a non-slotted suspendable CSMA-CA algorithm or a slotted suspendable CSMA-CA algorithm.

15. The network device of claim 13 , wherein the backoff suspend permission is determined by the network manager, a region regulator, an application developer, or a combination thereof.

16. A network device as described in Claim 15, wherein the network device is granted the backoff suspend permission by the network manager.

17. The network device of claim 16 , wherein other network devices choose not to perform the backoff suspend even if the backoff suspend is permitted.

18. The network device performs the backoff suspend to execute the active CCA within each of the unit backoff periods, suspends the backoff process when a channel is detected to be busy, and when the number of backoffs exceeds the threshold macMaxCSMABackoffs or the backoff time exceeds the threshold macSuspendedCSMAMaxTime, the suspendable CSMA / CA channel access mechanism The network device of claim 13 fails.

19. The network device first runs suspendable CSMA / CA and sets the unit backoff period (NUBP) to a random number in the range [0, 2 ＢＥ -1], and then the active CCA is performed within each of the unit backoff periods, and if the channel is busy, the backoff process is suspended (i.e., the NUBP is not decreased), and if the channel is free, the backoff process continues, and the backoff process is completed when the NUBP reaches zero.

20. The network device of claim 18 , wherein the network device performs a standard CCA within a CCA period when the number of unit backoff periods (NUBP) reaches zero.

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